D-Claw is an extension of the software package GeoClaw (www.clawpack.org) for simulating flows of granular-fluid mixtures with evolving volume fractions. It was developed primarily for landslides, debris flows and related phenomena by incorporating principles of solid, fluid and soil mechanics. However, because the two-phase model accommodates variable phase concentrations, it can also be used to model fluid problems in the absence of solid content (the model equations reduce to the shallow water equations as the solid phase vanishes). We therefore use D-Claw to seamlessly simulate multifaceted problems that involve the interaction of granular-fluid mixtures and bodies of water. This includes a large number of cascading natural hazards, such as debris-avalanches and lahars that enter rivers and lakes, landslide-generated tsunamis, landslide dams and outburst floods that entrain debris, and debris-laden tsunami inundation. I will describe the basis of D-Claw's model equations and highlight some recent applications, including the 2015 Tyndall Glacier landslide and tsunami, potential lahars on Mt. Rainier that displace dammed reservoirs, and a hypothetical landslide-generated lake outburst flood near Sisters, Oregon.